Sulfonylbis(phthalic anhydride) (SPAN), also known as 3,3',4,4'-sulfonylbis(phthalic anhydride) and as 3,3',4,4'-diphthalic anhydride sulfone, is a useful chemical intermediate that is particularly suitable for production of polymers with enhanced physical properties. For example, such dianhydride is useful for preparing polyimides. Also, polymers incorporating such dianhydride can be prepared with useful blending properties in polyether ketone formulations. If desired, such dianhydride can be converted to an ester which can then be used in the manufacture of polymers, such as polyimide resins, and the like. For such purposes, such dianhydride typically must have relatively high purity. Also, from the standpoint of commercial practically, such product must be producible in a relatively high yield from an economical process.
One possibly promising route for the preparation of SPAN could involve the oxidation of 3,3',4,4'-tetramethyl diphenyl sulfone (TMPS), also known as 3,3',4,4'-dixylyl sulfone, to the corresponding acid, sulfonyl bis(phthalic acid) (SBPA), also known as 3,3',4,4'-sulfonyl bis(phthalic acid), 3,3',4,4'-diphthalic acid sulfone, and as bis(3,4-dicarboxyphenyl) sulfone, followed by the dehydration of this acid to the desired dianhydride. Such an alkyl aromatic oxidation process is provided by the so-called "Mid-Century Oxidation Process" which is generally described by Towle et al in "Make Most Aromatic Acids Using Mid-Century Oxidation Processes," appearing in "Petrochemical Developments," 1964 Vol. 43, No. 11, pp. 149-152. See also U.S. Pat. Nos. 3,064,044 to Baldwin, 4,081,464 to Marsh et al, and 4,587,355 to Brown et al. Also, Japanese Kokai Tokyo Koho Patent Publication No. 88,185,939 of Aug. 1, 1988, based on Japanese patent application 87/14,365 filed Jan. 24, 1987 to Nakazawa et al [also in CA 110 (14):1154920], describes a process for oxidation of TMPS to SBPA in an aqueous acetic acid/solution using a heavy metal-and-bromine catalyst system, such as a cobalt/manganese/bromine catalyst.
The Nakazawa et al disclosure contains no teaching concerning the use of a zirconium-containing catalyst, the purification of SBPA, or the direct dehydration of solid SBPA to SPAN.
When a Mid-Century oxidation of TMPS to SBPA was carried out semicontinuously with a cobalt/manganese/bromine catalyst in an acetic acid/water solution, an SBPA purity of only 81.6% was achieved (see Example 6 hereinbelow), not a sufficient purity for use in making therefrom by direct solid state dehydration SPAN for polymer applications.
The prior art processes for dehydrating a polycarboxylic acid, such as SBPA, to SPAN utilize a liquid phase process. For example, dehydration of bis(3,4-dicarboxyphenoxyphenyl) sulfone to bis(3,4-dicarboxyphenoxyphenyl) sulfone dianhydride in acetic anhydride solution is described in U.S. Pat. No. 3,812,159 to Lubowitz. Purification and/or dehydration of an aromatic polycarboxylic acid, such as SBPA, in an organic solvent in the presence of activated carbon is taught in U.S. Pat. No. 4,370,487 to Meyer et al. A thermal dehydration of impure diphenyl sulfone carboxylic acids, such as crude SBPA, is taught in "Synthesis of Diaryl Sulfones and polycarboxylic acids Based on Them" by Mironow et al in Izv. Yyosh. Ucheb. Zaved., Khim. Khim. Tekhnol., 12 (11), 1588-93 (1969), CA72 (17): 89981c. While a solid phase dehydration to a relatively high purity product would be more desirable, so far as now known, the direct solid state dehydration of already highly purified SBPA to SPAN is not taught or accomplished in the prior art.
A new and improved process for converting TMPS to SPAN in high yield and in a purity sufficient for most known polymer applications would be economically advantageous. The present invention provides such a process.